Near infrared absorbing dyes find widespread use in imaging and information storage, particularly when information is to be written or read by means of a laser diode or similar source. As well as the conventional photographic applications such as sensitisation, acutance and antihalation, NIR dyes find increasing use in the conversion of radiant energy to thermal energy in systems such as optical data storage (by ablation of dyed polymer layers) and laser-addressed thermal transfer imaging.
Tetra-arylpolymethine dyes have found use in many of these systems, as disclosed, for example, in U.S. Pat. Nos. 4,547,444, 5,135,842 and 4,950,639.
In certain systems, notably in optical data storage, it is desirable to have the dye present in a coated layer in accordance with a predetermined pattern. For example, in optical discs it is necessary to provide servo tracking information to enable the read/write head to find any specified location on the disc with precision. This may be achieved by forming the storage media as a series of narrowly spaced concentric rings. Recently, the need has arisen to provide similar laser-readable information as an additional layer on otherwise conventional magnetic data storage media as disclosed, for example, in our co-pending U.S. application Ser. No. 08/152,811.
A potentially attractive route for forming such a predetermined pattern of NIR dye is to create the dye by photochemical reaction of its precursors in response to image-wise light exposure. Unfortunately, very few suitable systems are known which allow such image-wise formation of NIR dye. European Patent No. 68876 discloses photoimagable oxoinodolizine dyes which are NIR absorbing. The dyes are formed by a thermal reaction between cyclopropenone derivatives and certain pyridine derivatives. Selective photolysis of the cyclopropenone prior to thermal processing inhibits dye formation in light struck areas.
The present invention provides an alternative photoimagable dye class, with the formation of dye enabled, rather than disabled, in the light struck areas.